Electric circuit and fuse tester



Aug. 13, 1929. l.. H GARAUX ELECTRI CIRCUIT AND FUSE` TESTER vFiled. Sepb. 21, 1925 Arroz/Vix Ycreased current' -iwithout heating, hence its y that the greater the impressed. voltage, the

greater the resistance through the resistor 3 and the lamp 20, and the greater will be the flow of current through-the resistor.2.

This actioirfmay be illustrated as follows:

Voltage Temperature Resistance l 4 1 30 degrees C. (roon1temp.).'.. 2 ohms 100 700 degrees C. (room temp.)..- 6.834 ohms B00 2830 degrees C. (room temp.).. 26.52 ohms andso on, up to 3600 degrees the 'fusing point of tungsten. The temperature of resistor 2 remains constant,as the resistor 1s `built to carry any currentnecessary without heating. Thereforethe ratios for `the various impressed voltages are as follows:

At 100 volts resistor 2, 4 ohms, lamp 20, 6.83 ohms. At 600 volts resistor 2, 4 ohms, lamp 20, 28.52 ohms.

-The resistor increases in temperature' about 300 degrees centigrade and being constructed of nichrome resistance wire with a temperature coeicient of electrical` resistivity of .000432, and a normal resistance cold of 400 .ohms will have a resistance of hl-lohms at 300 degrees centigrade.

us: a

'lhe larger the temperature coeliicient of resistivity of the resistance material used in the resistorl 3 and the lamp filament, and

.the smaller lthe temperature .coeiicient of resistivity in the material used in the resistor 2, the greater will be theveiliciency of the tester; and -theusmaller the difference in the variation of the current flowing through the lamp 20, the greater the ran e of voltage over'which it may be used. An the greater lthe chan e of temperature inthe resistor 3, and the y temperature of the resistor 2 remains con-l stant, the greater the eiciency' of the `tester.

lament of thelamp 20 while the Thus the temperature coeiiicients of the materials used and the vary' temperature of these materials under diierent impressed voltages allows a four volt lamp to be used a range of about five hundred and vo ts.

e esistor 2 has approximately double the carrying capacity of the resistor 3 so thatin the operation .of the device, theresistor 2 will not heat and its resistance re- Owing tothe. fact that this windings constituting the resistance coils 2 and 3 are inductive, sharp breaking of the circuit at the terminals when the tester is in use will create a spark in accordance withvthe operation of Lenz law by virtue of which fact the tester may be used effectively even though the lamp ma be broken.

The windings an other elements of the tester areprotected by an outer tube ory casing C whlchmay be secured thereover in any suitable manner.

' Havin described my invention, I claim:

l. circuit and fuse tester comprising an inductively wound series resistor, and inductively wound shunt resistor, each having a ositive temperature coeicient, and a lam aving a high positive temperature coe cient; said shunt resistor and lamp being connectedin parallel and the series resistor being in series therewith,the shunt resistor having a currentcarrying capacity in excess of that of the series resistor.

, 2. fA circuit and fuse tester com rising a series resistor, a shunt resistor, an a lamp, said resistors and lamp each having a positive temperature coeicient that ofthe lam being greater than that of the Jresistors, sai series resistor having a resistance `man times that of the shunt resistor,., and sai shunt resistor and lamp being connected in parallel and the series resistor being in series therewith whereby a wide ranve of voltages may be determined automatically b virtue of the increase in resistance throng temperature rise in the series resistor.

' 3. A circuit and fuse tester comprising a cartridge having Jwithin it an inductively vwound series resistor and an .inductively wound shunt resistor, theA shunt resistor having a current carrying capacity greatly in excess of the series resistor, a lamp mounted one end of the cartridge and connected in parallel with the shunt resistor, the series resistor bein in series withlamp and shunt ,resistor an suitable terminals ,leading from said cartridge. y 4. A circuit and fuse tester for `use on comparatively low voltages 'comprising a seriesresistor, a shunt resistor, and a lamp, said series and shunt resistors having relatively llow and high conductivity and each having a positive temperature coeiicient, the series resistor being in series with the lamp and shunt resistor the shunt resistor being *connected in parallel with the lamp and having a tem erature coeiicient of low value lrelatlve to t e lamp wherebycurrent in excess of that necessary to light the lamp will flow through the shunt reslstor. i

In testimony whereof I hereunto aiiix my mains at a constant value while the .resignature. r

sistance of the `resistor 3 and the lafnp 20 is' increased by the heating of these elements,

LAWRENE H. GARAUX. 

